The present invention relates to a method of producing an adherent metallic coating on a steel sheet product.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Profiled structures made of steel sheet are coated to improve their properties, particularly for preventing corrosion or reducing wear. Various processes have been used to apply adherent layers of formless nature on metallic surfaces, such as sheets. Examples of such processes include hot galvanizing, electrogalvanizing, metal spraying of zinc, or sherardizing.
European patent document EP 1 013 785 A1 describes a method for coating a hot-rolled sheet steel with a metal or metal alloy, such as aluminum, by a dipping process. A blank is cut to size from the sheet steel and subjected to a temperature increase to initiate the forming process. As a result, an intermetallic phase is created on the surface for protection of the steel against corrosion and decarburation. After forming the sheet steel, the hot-formed steel sheet structure is cooled to confer hardness.
German patent document DE 102 24 319 A1 describes a method of making a coated structure for the automobile construction. A strip of hardenable steel or a blank from the strip is first coated with a metal or metal alloy in a process causing physical-mechanical bonding. The blank is then cold-formed and then hot-formed and hardened.
A problem associated with conventional methods is their limitation when hot formed steel sheet products are involved in order to produce a metallic surface coating. A reason resides in the necessary heating phase for the hot forming process. Pre-galvanizing, typically required for steel sheets, is not possible or only possible to a limited extent because zinc would be melted away during the heating phase. Although theoretically galvanizing may be carried out later, this however is time-consuming and complicates the overall construction and logistics. In addition, the result would be excessive layer thicknesses which render a welding of steel sheet products virtually impossible. While electrogalvanizing could conceivably provide thinner layer thicknesses, there is still the problem that high-strength steels cannot be coated as a result of hydrogen embrittlement which leads to premature crack formation.
It would therefore be desirable and advantageous to provide an improved method of producing an adherent metallic coating on a steel sheet product to obviate prior art shortcomings and to produce a coating, which can be realized with a defined layer thickness in a simple and economical manner and permits subsequent welding operations.